This invention relates generally to dynamo-electric machines and, more particularly, to processes for reducing vibration in motors during start-up and operation.
Electric motors are used in countless varieties and applications worldwide. Typically, torque generated at a rotor, which supplies the rotational force, is the product of current applied to the motor and an electromotive force generated by the application of a voltage to the coils of the motor. Motors generate torque in order to do work, that is, typically to drive a load.
In some applications, depending upon motor mounting or other factors, the generated torque, together with the load, may cause a motor to vibrate and generate noise as the motor begins to move its load. One example of such an application is where the motor is driving a fan as its load. Imbalances in the fan combined with torque pulses produce vibrations which are conducted to the motor and fan mounting, producing undesirable noise. Damping systems are typically employed to minimize the effects of the vibrational energy induced into the motor and fan system. Such damping system are expensive and tend to deteriorate over time due to exposure to the elements and continued exposure to vibrational energy, leading to loosened motor and fan assemblies, potentially leading to failures of the motor or the fan.
In some applications, the problem is most prevalent at startup. However, once the motor is up to speed however, the noise and vibrations lessen or disappear. In many applications, the motor generated noise and vibrations at startup are undesirable. In other applications, such as the fan example described above, the noise and vibration problems are always present. It would be desirable to control motor startup and operation to eliminate the problem of high torque vibration and noise, allowing the possibility of eliminating damping systems, and reducing costs.
In an exemplary embodiment, a motor control system includes a microprocessor programmed to apply current to an electrical motor. The microprocessor pulse width modulates the current so that reductions in peak currents and the filtering of fundamental frequencies reduce the amount of torque generated by the motor. Reductions in torque reduce vibrations and noise of the motor thereby allowing reductions or elimination of damping systems. The method for minimizing electrical machine vibration includes the steps of applying power to the motor under microprocessor control such that a pulse width modulated current profile is applied to the motor.